Air traffic controllers direct a pilot to maintain a fixed spacing or interval, in time or distance, between their aircraft and a specified, preceding aircraft, e.g. when both aircraft are on the same landing approach to an airport. Air traffic controllers periodically need to instruct aircraft to slow down or speed up to maintain the interval. This is a burden on both the air traffic controllers who must provide updated instructions to aircraft pilots. Because such information is not provided in real time, aircraft may travel too fast, and thus having inadequate spacing with the proceeding aircraft. This increases the risk of an accident. Also, it is not efficient, as air traffic controllers have to divert such aircraft whose interval is too small, and forcing the aircraft to recommence its landing approach.
To help automate this process, aircraft are being equipped with automatic dependent surveillance-broadcast transmitters (ADS-B Out) which broadcast aircraft speed, direction, and position to receivers (ADS-B In) in aircraft and one the ground. Aircraft equipped with ADS-B In are made aware of the presence and location of other nearby aircraft using ADS-B Out. For aircraft equipped with it, ADS-B In provides a backup for traffic alert and collision avoidance systems. Also, ADS-B In provides guidance for pilots landing aircraft in a paired approach, with another aircraft, to two closely spaced runways.
Some aircraft are equipped with flight deck interval management (FIM) systems in addition to ADS-B In. In landing approaches, the FIM system generates, in real time, the speed at which the aircraft should fly to maintain the mandated interval, which better permits a pilot to maintain the interval.
Some aircraft, however, are not equipped with a FIM system, and thus cannot benefit from FIM. This undermines the desired safety and efficiency improvements made available by ADS-B Out. Therefore, there is a need to allow aircraft lacking a FIM system to benefit from FIM.